EDP Sciences
Free access
Volume 424, Number 3, September IV 2004
Page(s) 1049 - 1053
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20041380

A&A 424, 1049-1053 (2004)
DOI: 10.1051/0004-6361:20041380

Asymmetrical appearance of dark-cored filaments in sunspot penumbrae

P. Sütterlin1, L. R. Bellot Rubio2 and R. Schlichenmaier2

1  Sterrekundig Instituut Utrecht, Postbus 80 000, 3508 TA Utrecht, The Netherlands
    e-mail: P.Suetterlin@astro.uu.nl
2  Kiepenheuer Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany

(Received 1 June 2004 / Accepted 2 June 2004)

Recent sunspot observations at unprecedented resolution have led to the discovery of dark cores in the bright filaments that form the penumbra (Scharmer et al. 2002). The discovery paper considered spots at disk center only, so the properties of the dark-cored filaments remain largely unknown. Here we analyze a speckle-reconstructed time series of G-band and blue continuum images of a sunspot acquired with the Dutch Open Telescope. The target was located at an heliocentric angle of 27 deg. We confirm the existence of dark-cored penumbral filaments also in spots outside the disk center, and report on distinct differences between the center and limb-side penumbra. In the inner center-side penumbra, filaments are detected as two narrow bright streaks separated by a central obscuration. These structures move together as a single entity. On the limb side, dark cores are hardly seen. The time series is used to determine the sizes (~200-250 km), proper motions (~280 m s -1), and lifetimes ( $\la$ 45 min) of typical dark-cored filaments.

Key words: Sun: sunspots -- Sun: magnetic fields -- Sun: photosphere -- magnetohydrodynamics

© ESO 2004